Parallelize address scanning and unify address display formatting

Scanning: check all gap-limit addresses in parallel per batch instead
of sequentially. For a wallet with 1 used address this reduces from
12 sequential RPC round-trips to 1 parallel batch + 1 small follow-up.

Display: add shared formatAddressHtml(address, ensName, maxLen) and
escapeHtml() to helpers.js. Use them in confirm-tx (was missing color
dot entirely) and approval view. Remove duplicate escapeHtml from
addressDetail.js.

src/shared/balances.js

@@ -166,44 +166,54 @@ async function lookupTokenInfo(contractAddress, rpcUrl) {
 }
 
 // Derive HD addresses starting from index 0 and check for on-chain activity.
-// Stops after gapLimit consecutive addresses with zero balance and zero tx count.
+// Checks gapLimit addresses in parallel per batch.  Stops when an entire
+// batch has no used addresses (i.e. gapLimit consecutive empty addresses).
 // Returns { addresses: [{ address, index }], nextIndex }.
 async function scanForAddresses(xpub, rpcUrl, gapLimit = 5) {
     log.debugf("scanForAddresses start, gapLimit:", gapLimit);
     const provider = getProvider(rpcUrl);
     const used = [];
-    let gap = 0;
-    let index = 0;
+    let checked = 0;
+    let checkUpTo = gapLimit;
 
-    while (gap < gapLimit) {
-        const addr = deriveAddressFromXpub(xpub, index);
-        let balance, txCount;
-        try {
-            [balance, txCount] = await Promise.all([
-                provider.getBalance(addr),
-                provider.getTransactionCount(addr),
-            ]);
-        } catch (e) {
-            log.errorf(
-                "scanForAddresses check failed",
-                addr,
-                e.shortMessage || e.message,
-            );
-            // Treat RPC failure as empty to avoid infinite loop
-            gap++;
-            index++;
-            continue;
+    while (checked < checkUpTo) {
+        const batch = [];
+        for (let i = checked; i < checkUpTo; i++) {
+            const addr = deriveAddressFromXpub(xpub, i);
+            batch.push({ addr, index: i });
         }
-        if (balance > 0n || txCount > 0) {
-            used.push({ address: addr, index });
-            gap = 0;
-            log.debugf("scanForAddresses used", addr, "index:", index);
-        } else {
-            gap++;
+
+        const results = await Promise.all(
+            batch.map(async ({ addr, index }) => {
+                try {
+                    const [balance, txCount] = await Promise.all([
+                        provider.getBalance(addr),
+                        provider.getTransactionCount(addr),
+                    ]);
+                    return { addr, index, isUsed: balance > 0n || txCount > 0 };
+                } catch (e) {
+                    log.errorf(
+                        "scanForAddresses check failed",
+                        addr,
+                        e.shortMessage || e.message,
+                    );
+                    return { addr, index, isUsed: false };
+                }
+            }),
+        );
+
+        checked = checkUpTo;
+
+        for (const r of results) {
+            if (r.isUsed) {
+                used.push({ address: r.addr, index: r.index });
+                log.debugf("scanForAddresses used", r.addr, "index:", r.index);
+                checkUpTo = Math.max(checkUpTo, r.index + 1 + gapLimit);
+            }
         }
-        index++;
     }
 
+    used.sort((a, b) => a.index - b.index);
     const nextIndex = used.length > 0 ? used[used.length - 1].index + 1 : 1;
     log.infof(
         "scanForAddresses done, found:",